In this portion of a letter, Elder Sophrony writes regarding holy oil and how to use it. Specifically, he refers to Holy Unction, but this could apply to all holy oil as well:
"I am glad that your cheek is better. You should anoint it with the oil that you have now. And you should do so in the following way:
You should take some oil on the tip of your finger, and make the sign of the Cross on the sick body part and say:
'In the name of the Father and the Son and the Holy Spirit…O Lord, heal my spiritual and bodily afflictions, and save me, in the manner that You know.'
Then, you should rub it into the sick body part. This you should do to every bodily member that is suffering. Regardless of whether you are healed or not, you should do this to be sanctified.
I have experienced, however, a multitude of cases of astonishing healing. This holy oil [i.e. the Sacrament of Holy Unction] is especially sanctified. It is sanctified on Wednesday or Thursday of Holy Week…"
From the book: Letters from Russia, by Archimandrite Sophrony Sacharov, published by the Holy Monastery of the Precious Forerunner, Essex, England. (source)